Organic light-emitting devices (OLED), as a new type of display technology, have unique advantages such as self-illumination, wide viewing angle, low power consumption, high efficiency, thin, rich colors, fast response, extensive application temperature, low drive voltage, used to make flexible, bendable and transparent display panel and environmental friendliness, etc. Therefore, OLED technology can be applied to flat panel displays and new generation of lighting, or can be used as backlight of LCD. Since 1987, Kodak (Tang et al) made sandwich bilayer devices using 8-hydroxyquinoline aluminum (Alq3) as a light emitting layer, triphenylamine derivative as a hole transporting layer through thin-film vacuum evaporation technique. Under 10V driving voltage, the luminance is up to 1000 cd/m2 (Tang C. W, Vanslyke S. A. Appl. Phys. Lett. 1987, 51, 913-916). This technological breakthrough has aroused widespread concern in the scientific community and industry, and organic light-emitting research and applications become a hot issue. Subsequently, in 1989, with the invention of host and guest material technology, the luminous efficiency and lifetime of OLED is greatly improved. In 1998, Ma Yuguang and Zhi Zhiming, et al found the electroluminescent phosphorescence phenomenon, which broke through the theoretical limit of organic electroluminescent quantum efficiency less than 25%, rising to 100% (Synthetic Metals 94 (1998) 245-248). Since then, the organic light-emitting entered into a new era, extending the field of research.
A classic OLED comprises a cathode and an anode, which includes a hole transport layer, a light emitting layer and an electron transport layer. The holes generating from the anode through the hole transport layer and the electrons generating from the cathode through the electron transport layer combine to form excitons in the light emitting layer, emitting light. 2,6-bis[3′-(N-carbazolyl)phenyl]pyridine (DCzPPy) was firstly developed by Kido and used as a bipolar host material in 2008; together with Flrpic, it is used in efficient blue phosphorescent organic light emitting diodes as a dopant (Chem. Mater. 2011, 23, 274-284). Jeong-Ik Lee made white-light OLED using DCzPPy. In combination with the unique molecular structures of carbazole electron donors with high triplet energy and eletron receptor pyridine with high electron affinity, DCzPPy is important bipolar host material of highly-efficient blue and white phosphorescent OLED (Adv. Mater. 2010, 22, 5003-5007).
The conventionally reported method for synthesis of DCzPPy (Chem. Mater. 2008,20,1691-1693) requires expensive palladium catalyst that may causes high production cost, and all experimental procedures require metal catalysts in the overall three-step synthesis steps, thereby increasing the risk of metal contamination of the final products. In addition, the intermediates and final products must be purified by column chromatography, difficult to be applied in mass production.